Atlantic Monthly, Vol. 9, No. 54, April, 1862 by Various
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Various >> Atlantic Monthly, Vol. 9, No. 54, April, 1862
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_Naked Reptiles_. Toads and Frogs, Salamanders, Caecilians.
_Scaly Reptiles._ Turtles, Lizards, Serpents.
Such corresponding groups or parallel types, united only by external
resemblance, and distinguished from each other by essential elements of
structure, exist among all animals, though they are less striking among
Birds on account of the uniformity of that class. Yet even there we may
trace such analogies,--as between the Palmate or Aquatic Birds, for
instance, and the Birds of Prey, or between the Frigate Bird and the
Kites. Among Fishes such analogies are very common, often suggesting a
comparison even with land animals, though on account of the scales and
spines of the former the likeness may not be easily traced. But the
common names used by the fishermen often indicate these resemblances,
--as, for instance, Sea-Vulture, Sea-Eagle, Cat-Fish, Flying-Fish,
Sea-Porcupine, Sea-Cow, Sea-Horse, and the like. In the branch of
Mollusks, also, the same superficial analogies are found. In the lowest
class of this division of the Animal Kingdom there is a group so similar
to the Polyps, that, until recently, they have been associated with
them,--the Bryozoa. They are very small animals, allied to the Clams by
the plan of their structure, but they have a resemblance to the Polyps
on account of a radiating wreath of feelers around the upper part of
their body: yet, when examined closely, this wreath is found to be
incomplete; it does not, form a circle, but leaves an open space between
the two ends, where they approach each other, so that it has a horseshoe
outline, and partakes of the bilateral symmetry characteristic of its
type and on which its own structure is based. These series have not yet
been very carefully traced, and young naturalists should turn their
attention to them, and be prepared to draw the nicest distinction
between analogies and true affinities among animals.
VIII.
After this digression, let us proceed to a careful examination of the
natural groups of animals called Families by naturalists,--a subject
already briefly alluded to in a previous chapter. Families are natural
assemblages of animals of less extent than Orders, but, like Orders,
Classes, and Branches, founded upon certain categories of structure,
which are as distinct for this kind of group as for all the other
divisions in the classification of the Animal Kingdom.
That we may understand the true meaning of these divisions, we must not
be misled by the name given by naturalists to this kind of group. Here,
as in so many other instances, a word already familiar, and that had
become, as it were, identified with the special sense in which it
had been used, has been adopted by science and has received a new
signification. When naturalists speak of Families among animals, they do
not allude to the progeny of a known stock, as we designate, in common
parlance, the children or the descendants of known parents by the word
family; they understand by Families natural groups of different kinds
of animals, having no genetic relations so far as we know, but agreeing
with one another closely enough to leave the impression of a more
or less remote common parentage. The difficulty here consists in
determining the natural limits of such groups, and in tracing the
characteristic features by which they may be defined; for individual
investigators differ greatly as to the degree of resemblance existing
between the members of many Families, and there is no kind of
group which presents greater diversity of circumscription in the
classifications of animals proposed by different naturalists than these
so-called Families.
It should be remembered, however, that, unless a sound criterion be
applied to the limitation of Families, they, like all other groups
introduced into zooelogical systems, must forever remain arbitrary
divisions, as they have been hitherto. A retrospective glance at the
progress of our science during the past century, in this connection,
may perhaps help us to solve the difficulty. Linnaeus, in his System
of Nature, does not admit Families; he has only four kinds of
groups,--Classes, Orders, Genera, and Species. It was among plants that
naturalists first perceived those general traits of resemblance which
exist everywhere among the members of natural families, and added this
kind of group to the framework of their system. In France, particularly,
this method was pursued with success; and the improvements thus
introduced by the French botanists were so great, and rendered their
classification so superior to that of Linnaeus, that the botanical
systems in which Families were introduced were called natural systems,
in contradistinction especially to the botanical classification of
Linnaeus, which was founded upon the organs of reproduction, and which
received thenceforth the name of the sexual system of plants. The same
method so successfully used by botanists was soon introduced
into Zooelogy by the French naturalists of the beginning of this
century,--Lamarck, Latreille, and Cuvier. But, to this day, the
limitation of Families among animals has not yet reached the precision
which it has among plants, and I see no other reason for the difference
than the absence of a leading principle to guide us in Zooelogy.
Families, as they exist in Nature, are based upon peculiarities of form
as related to structure; but though a very large number of them have
been named and recorded, very few are characterized with anything like
scientific accuracy. It has been a very simple matter to establish such
groups according to the superficial method that has been pursued, for
the fact that they are determined by external outline renders the
recognition of them easy and in many instances almost instinctive; but
it is very difficult to characterize them, or, in other words, to trace
the connection between form and structure. Indeed, many naturalists do
not admit that Families are based upon form; and it was in trying to
account for the facility with which they detect these groups, while they
find it so difficult to characterize them, that I perceived that they
are always associated with peculiarities of form. Naturalists have
established Families simply by bringing together a number of animals
resembling each other more or less closely, and, taking usually the name
of the Genus to which the best known among them belongs, they have given
it a patronymic termination to designate the Family, and allowed the
matter to rest there, sometimes without even attempting any description
corresponding to those by which Genus and Species are commonly defined.
For instance, from _Canis_, the Dog, _Canidae_ has been formed, to
designate the whole Family of Dogs, Wolves, Foxes, etc. Nothing can be
more superficial than such a mode of classification; and if these
groups actually exist in Nature, they must be based, like all the other
divisions, upon some combination of structural characters peculiar to
them. We have seen that Branches are founded upon the general plan of
structure, Classes on the mode of executing the plan, Orders upon the
greater or less complication of a given mode of execution, and we shall
find that form, as _determined by structure_, characterizes Families. I
would call attention to this qualification of my definition; since, of
course, when speaking of form in this connection, I do not mean those
superficial resemblances in external features already alluded to in
my remarks upon Parallel or Collateral Types. I speak now of form as
controlled by structural elements; and unless we analyze Families in
this way, the mere distinguishing and naming them does not advance our
science at all. Compare, for instance, the Dogs, the Seals, and the
Bears. These are all members of one Order,--that of the Carnivorous
Mammalia. Their dentition is peculiar and alike in all, (cutting teeth,
canine teeth, and grinders,) adapted for tearing and chewing their
food; and their internal structure bears a definite relation to their
dentition. But look at these animals with reference to form. The Dog is
comparatively slender, with legs adapted for running and hunting his
prey; the Bear is heavier, with shorter limbs; while the Seal has a
continuous uniform outline adapted for swimming. They form separate
Families, and are easily recognized as such by the difference in their
external outline; but what is the anatomical difference which produces
the peculiarity of form in each, by which they have been thus
distinguished? It lies in the structure of the limbs, and especially in
that of the wrist and fingers. In the Seal the limbs are short, and the
wrists are on one continuous line with them, so that it has no power of
bending the wrist or the fingers, and the limbs, therefore, act like
flappers or oars. The Bear has a well-developed paw with a flexible
wrist, but it steps on the whole sole of the foot, from the wrist to the
tip of the toe, giving it the heavy tread so characteristic of all the
Bears. The Dogs, on the contrary, walk on tip-toe, and their step,
though firm, is light, while the greater slenderness and flexibility of
their legs add to their nimbleness and swiftness. By a more extensive
investigation of the anatomical structure of the limbs in their
connection with the whole body, it could easily be shown that the
peculiarity of form in these animals is essentially determined by, or at
least stands in the closest relation to, the peculiar structure of the
wrist and fingers.
Take the Family of Owls as distinguished from the Falcons, Kites, etc.
Here the difference of form is in the position of the eyes. In the
Owl, the sides of the head are prominent and the eye-socket is brought
forward. In the Falcons and Kites, on the contrary, the sides of the
head are flattened and the eyes are set back. The difference in the
appearance of the birds is evident to the most superficial observer; but
to call the one Strigidae and the other Falconidae tells us nothing of
the anatomical peculiarities on which this difference is founded.
These few examples, selected purposely among closely allied and
universally known animals, may be sufficient to show, that, beyond the
general complication of the structure which characterizes the Orders,
there is a more limited element in the organization of animals, bearing
chiefly upon their form, which, if it have any general application as
a principle of classification, may well be considered as essentially
characteristic of the Families. There are certainly closely allied
natural groups of animals, belonging to the same Order, but including
many Genera, which differ from each other chiefly in their form, while
that form is determined by peculiarities of structure which do not
influence the general structural complication upon which Orders are
based, or relate to the minor details of structure on which Genera are
founded. I am therefore convinced that form is the criterion by which
Families may be determined. The great facility with which animals may
be combined together in natural groups of this kind without any special
investigation of their structure, a superficial method of classification
in which zooelogists have lately indulged to a most unjustifiable degree,
convinces me that it is the similarity of form which has unconsciously
led such shallow investigators to correct results, since upon close
examination it is found that a large number of the Families so
determined, and to which no characters at all are assigned, nevertheless
bear the severest criticism founded upon anatomical investigation.
The questions proposed to themselves by all students who would
characterize Families should be these: What are, throughout the
Animal Kingdom, the peculiar patterns of form by which Families are
distinguished? and on what structural features are these patterns based?
Only the most patient investigations can give us the answer, and it will
be very long before we can write out the formulae of these patterns with
mathematical precision, as I believe we shall be able to do in a more
advanced stage of our science. But while the work is in progress, it
ought to be remembered that a mere general similarity of outline is not
yet in itself evidence of identity of form or pattern, and that, while
seemingly very different forms may be derived from the same formula, the
most similar forms may belong to entirely different systems, when their
derivation is properly traced. Our great mathematician, in a lecture
delivered at the Lowell Institute last winter, showed that in his
science, also, similarity of outline does not always indicate identity
of character. Compare the different circles,--the perfect circle, in
which every point of the periphery is at the same distance from the
centre, with an ellipse in which the variation from the true circle is
so slight as to be almost imperceptible to the eye; yet the latter, like
all ellipses, has its two _foci_ by which it differs from a circle,
and to refer it to the family of circles instead of the family of
ellipses would be overlooking its true character on account of its
external appearance; and yet ellipses may be so elongated, that, far
from resembling a circle, they make the impression of parallel lines
linked at their extremities. Or we may have an elastic curve in which
the appearance of a circle is produced by the meeting of the two ends;
nevertheless it belongs to the family of elastic curves, in which may
even be included a line actually straight, and is formed by a process
entirely different from that which produces the circle or the ellipse.
But it is sometimes exceedingly difficult to find the relation between
structure and form in Families, and I remember a case which I had taken
as a test of the accuracy of the views I entertained upon this subject,
and which perplexed and baffled me for years. It was that of our
fresh-water Mussels, the Family of Unios. There is a great variety of
outline among them,--some being oblong and very slender, others broad
with seemingly square outlines, others having a nearly triangular form,
while others again are almost circular; and I could not detect among
them all any feature of form that was connected with any essential
element of their structure. At last, however, I found this
test-character, and since that time I have had no doubt left in my mind
that form, determined by structure, is the true criterion of Families.
In the Unios it consists of the rounded outline of the anterior end of
the body reflected in a more or less open curve of the shell, bending
more abruptly along the lower side with an inflection followed by a
bulging, corresponding to the most prominent part of the gills, to which
alone, in a large number of American Species of this Family, the eggs
are transferred, giving to this part of the shell a prominence which it
has not in any of the European Species. At the posterior end of the body
this curve then bends upwards and backwards again, the outline meeting
the side occupied by the hinge and ligament, which, when very short, may
determine a triangular form of the whole shell, or, when equal to the
lower side and connected with a great height of the body, gives it a
quadrangular form, or, if the height is reduced, produces an elongated
form, or, finally, a rounded form, if the passage from one side to the
other is gradual. A comparison of the position of the internal organs of
different Species of Unios with the outlines of their shells will leave
no doubt that their form is determined by the structure of the animal.
A few other and more familiar examples may complete this discussion.
Among Climbing Birds, for instance, which are held together as a
more comprehensive group by the structure of their feet and by other
anatomical features, there are two Families so widely different in
their form that they may well serve as examples of this principle. The
Woodpeckers (_Picidae_) and the Parrots (_Psittacidae_), once considered
as two Genera only, have both been subdivided, in consequence of a more
intimate knowledge of their generic characters, into a large number of
Genera; but all the Genera of Woodpeckers and all the Genera of the
Parrots are still held together by their form as Families, corresponding
as such to the two old Genera of _Picus_ and _Psittacus_. They are now
known as the Families of Woodpeckers and Parrots; and though each group
includes a number of Genera combined upon a variety of details in the
finish of special parts of the structure, such as the number of toes,
the peculiarities of the bill, etc., it is impossible to overlook the
peculiar form which is characteristic of each. No one who is familiar
with the outline of the Parrot will fail to recognize any member of
that Family by a general form which is equally common to the diminutive
Nonpareil, the gorgeous Ara, and the high-crested Cockatoo. Neither will
any one, who has ever observed the small head, the straight bill, the
flat back, and stiff tail of the Woodpecker, hesitate to identify the
family form in any of the numerous Genera into which this group is now
divided. The family characters are even more invariable than the generic
ones; for there are Woodpeckers which, instead of the four toes, two
turning forward and two backward, which form an essential generic
character, have three toes only, while the family form is always
maintained, whatever variations there may be in the characters of the
more limited groups it includes.
The Turtles and Terrapins form another good illustration of family
characters. They constitute together a natural Order, but are
distinguished from each other as two Families very distinct in general
form and outline. Among Fishes I may mention the Family of Pickerels,
with their flat, long snout, and slender, almost cylindrical body, as
contrasted with the plump, compressed body and tapering tail of the
Trout Family. Or compare, among Insects, the Hawk-Moths with the Diurnal
Butterfly, or with the so-called Miller,--or, among Crustacea, the
common Crab with the Sea-Spider, or the Lobsters with the Shrimps,--or,
among Worms, the Leeches with the Earth-Worms,--or, among Mollusks,
the Squids with the Cuttle-Fishes, or the Snails with the Slugs, or the
Periwinkles with the Limpets and Conchs, or the Clam with the so-called
Venus, or the Oyster with the Mother-of-Pearl shell,--everywhere,
throughout the Animal Kingdom, difference of form points at difference
of Families.
There is a chapter in the Natural History of Animals that has hardly
been touched upon as yet, and that will be especially interesting with
reference to Families. The voices of animals have a family character not
to be mistaken. All the Canidae bark and howl: the Fox, the Wolf, the
Dog have the same kind of utterance, though on a somewhat different
pitch. All the Bears growl, from the White Bear of the Arctic snows to
the small Black Bear of the Andes. All the Cats _miau_, from our quiet
fireside companion to the Lions and Tigers and Panthers of the forest
and jungle. This last may seem a strange assertion; but to any one who
has listened critically to their sounds and analyzed their voices,
the roar of the Lion is but a gigantic _miau_, bearing about the same
proportion to that of a Cat as its stately and majestic form does to the
smaller, softer, more peaceful aspect of the Cat. Yet, notwithstanding
the difference in their size, who can look at the Lion, whether in his
more sleepy mood as he lies curled up in the corner of his cage, or in
his fiercer moments of hunger or of rage, without being reminded of a
Cat? And this is not merely the resemblance of one carnivorous animal to
another; for no one was ever reminded of a Dog or Wolf by a Lion. Again,
all the Horses and Donkeys neigh; for the bray of the Donkey is only a
harsher neigh, pitched on a different key, it is true, but a sound of
the same character,--as the Donkey himself is but a clumsy and dwarfish
Horse. All the Cows low, from the Buffalo roaming the prairie, the
Musk-Ox of the Arctic ice-fields, or the Jack of Asia, to the Cattle
feeding in our pastures. Among the Birds, this similarity of voice in
Families is still more marked. We need only recall the harsh and noisy
Parrots, so similar in their peculiar utterance. Or take as an example
the web-footed Family,--do not all the Geese and the innumerable host
of Ducks quack? Does not every member of the Crow Family caw, whether it
be the Jackdaw, the Jay, the Magpie, the Rook in some green rookery of
the Old World, or the Crow of our woods, with its long, melancholy caw
that seems to make the silence and solitude deeper? Compare all the
sweet warblers of the Songster Family,--the Nightingales, the Thrushes,
the Mocking-Birds, the Robins; they differ in the greater or less
perfection of their note, but the same kind of voice runs through the
whole group. These affinities of the vocal systems among animals form a
subject well worthy of the deepest study, not only as another character
by which to classify the Animal Kingdom correctly, but as bearing
indirectly also on the question of the origin of animals. Can we suppose
that characteristics like these have been communicated from one animal
to another? When we find that all the members of one zoological Family,
however widely scattered over the surface of the earth, inhabiting
different continents and even different hemispheres, speak with one
voice, must we not believe that they have originated in the places where
they now occur with all their distinctive peculiarities? Who taught the
American Thrush to sing like his European relative? He surely did not
learn it from his cousin over the waters. Those who would have us
believe that all animals have originated from common centres and single
pairs, and have been distributed from such common centres over the
world, will find it difficult to explain the tenacity of such characters
and their recurrence and repetition under circumstances that seem to
preclude the possibility of any communication, on any other supposition
than that of their creation in the different regions where they are now
found. We have much yet to learn in this kind of investigation, with
reference not only to Families among animals, but to nationalities among
men also. I trust that the nature of languages will teach us as much
about the origin of the races as the vocal systems of the animals may
one day teach us about the origin of the different groups of animals.
At all events, similarity of vocal utterance among animals is not
indicative of identity of Species; I doubt, therefore, whether
similarity of speech proves community of origin among men.
The similarity of motion in Families is another subject well worth the
consideration of the naturalist: the soaring of the Birds of Prey,--the
heavy flapping of the wings in the Gallinaceous Birds,--the floating of
the Swallows, with their short cuts and angular turns,--the hopping
of the Sparrows,--the deliberate walk of the Hens and the strut of the
Cocks,--the waddle of the Ducks and Geese,--the slow, heavy creeping
of the Land-Turtle,--the graceful flight of the Sea-Turtle under the
water,--the leaping and swimming of the Frog,--the swift run of the
Lizard, like a flash of green or red light in the sunshine,--the
lateral undulation of the Serpent,--the dart of the Pickerel,--the
leap of the Trout,--the rush of the Hawk-Moth through the air,--the
fluttering flight of the Butterfly,--the quivering poise of the
Humming-Bird,--the arrow-like shooting of the Squid through the water,
--the slow crawling of the Snail on the land,--the sideway movement
of the Sand-Crab,--the backward walk of the Crawfish,--the almost
imperceptible gliding of the Sea-Anemone over the rock,--the graceful,
rapid motion of the Pleurobrachia, with its endless change of curve and
spiral. In short, every Family of animals has its characteristic action
and its peculiar voice; and yet so little is this endless variety
of rhythm and cadence both of motion and sound in the organic world
understood, that we lack words to express one-half its richness and
beauty.
IX.
The well-known meaning of the words _generic_ and _specific_ may serve,
in the absence of a more precise definition, to express the relative
importance of those groups of animals called Genera and Species in our
scientific systems. The Genus is the more comprehensive of the two kinds
of groups, while the Species is the most precisely defined, or at least
the most easily recognized, of all the divisions of the Animal Kingdom.
But neither the term Genus nor Species has always been taken in the same
sense. Genus especially has varied in its acceptation, from the time
when Aristotle applied it indiscriminately to any kind of comprehensive
group, from the Classes down to what we commonly call Genera, till the
present day. But we have already seen, that, instead of calling all the
various kinds of more comprehensive divisions by the name of Genera,
modern science has applied special names to each of them, and we have
now Families, Orders, Classes, and Branches above Genera proper. If
the foregoing discussion upon the nature of these groups is based upon
trustworthy principles, we must admit that they are all founded upon
distinct categories of characters,--the primary divisions, or the
Branches, on plan of structure, the Classes upon the manner of its
execution, the Orders upon the greater or less complication of a given
mode of execution, the Families upon form; and it now remains to be
ascertained whether Genera also exist in Nature, and by what kind of
characteristics they may be distinguished. Taking the practice of the
ablest naturalists in discriminating Genera as a guide in our estimation
of their true nature, we must, nevertheless, remember that even now,
while their classifications of the more comprehensive groups usually
agree, they differ greatly in their limitation of Genera, so that the
Genera of some authors correspond to the Families of others, and vice
versa. This undoubtedly arises from the absence of a definite standard
for the estimation of these divisions. But the different categories of
structure which form the distinctive criteria of the more comprehensive
divisions once established, the question is narrowed down to an inquiry
into the special category upon which Genera may be determined; and if
this can be accurately defined, no difference of opinion need interfere
hereafter with their uniform limitation. Considering all these divisions
of the Animal Kingdom from this point of view, it is evident that the
more comprehensive ones must be those which are based on the broadest
characters,--Branches, as united upon plan of structure, standing of
course at the head; next to these the Classes, since the general mode
of executing the plan presents a wider category of characters than
the complication of structure on which Orders rest; after Orders come
Families, or the patterns of form in which these greater or less
complications of structure are clothed; and proceeding in the same way
from more general to more special considerations, we can have no other
category of structure as characteristic of Genera than the details of
structure by which members of the same Family may differ from each
other, and this I consider as the only true basis on which to limit
Genera, while it is at the same time in perfect accordance with the
practice of the most eminent modern zoologists. It is in this way that
Cuvier has distinguished the large number of Genera he has characterized
in his great Natural History of the Fishes, in connection with
Valenciennes. Latreille has done the same for the Crustacea and Insects;
and Milne Edwards, with the cooeperation of Haime, has recently proceeded
upon the same principle in characterizing a great number of Genera among
the Corals. Many others have followed this example, but few have kept
in view the necessity of a uniform mode of proceeding, or, if they have
done their researches have covered too limited a ground, to be taken
into consideration in a discussion of principles. It is, in fact, only
when extending over a whole Class that the study of Genera acquires a
truly scientific importance, as it then shows in a connected manner, in
what way, by what features, and to what extent a large number of animals
are closely linked together in Nature. Considering the Animal Kingdom as
a single complete work of one Creative Intellect, consistent throughout,
such keen analysis and close criticism of all its parts have the same
kind of interest, in a higher degree, as that which attaches to other
studies undertaken in the spirit of careful comparative research.
These different categories of characters are, as it were, different
peculiarities of style in the author, different modes of treating the
same material, new combinations of evidence bearing on the same general
principles. The study of Genera is a department of Natural History which
thus far has received too little attention even at the hands of our best
zoologists, and has been treated in the most arbitrary manner; it
should henceforth be made a philosophical investigation into the closer
affinities which naturally bind in minor groups all the representatives
of a natural Family.
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